The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Engines may operate in different modes under various operating conditions. For example, in a normal driving mode, a diesel engine combusts diesel fuel with air flowing through an intake manifold. Exhaust gases flow out of the engine through an exhaust manifold. Various exhaust treatment components treat the exhaust gases before they escape to the atmosphere. A turbocharger boosts air pressure in the intake manifold using energy from exhaust gas flow. An intake throttle valve (ITV) controls intake airflow.
Conversely, in an exhaust braking mode, the engine slows the vehicle by increasing exhaust backpressure and intake manifold pressure. The exhaust backpressure opposes movement of the pistons during the exhaust stroke, which applies braking forces through the driveline to slow the entire vehicle. The engine control module may stop fueling the cylinders to prevent any positive torque from being produced by combustion. A variable nozzle turbocharger (VNT) may be used to increase the exhaust backpressure by restricting exhaust flow. The ITV is opened, causing increased air mass to enter the intake side of the engine. Higher exhaust gas velocity and a high pressure differential through the turbine increase turbine speeds inside the VNT. In this manner, the pressure in the intake manifold forces more air into the cylinders, which further increases exhaust backpressure.